The Repel Fog ritual turns out to take just over half an hour under current conditions. It's a little tiring, but bearably so.
The moment it finishes is tangible to Sable as an abrupt release of tension, a pulling-away or closing-off of the pathway through which she was channeling magic into the Mana Font. To everyone else, it's audible as a rush of distant wind, and visible as a beam of sunlight through the porthole in the upper hatch.
The crystal at the bottom of the Mana Font has filled with blue light to a depth of maaaaaybe four inches. There is a whole lot of Mana Font left to fill.
Also, Sable feels a bit low on mana, a sort of hollow sensation located in the part of her mind she's been channeling all this magic out of. It might be time for the Restoring Mana procedure scribbled in the margin of the wands section, which approximately says to reach out through your wand like you're trying to find a target to channel magic into, connect to the Mana Font or a secondary reservoir, and pull. It shouldn't take more than a few seconds to refill even a very depleted mage.